1. Field of the Invention
The present invention relates to an active visibility support apparatus and an active visibility support method for a vehicle which are used to allow a driver to more properly identify an object to be viewed while driving a vehicle.
2. Description of Related Arts
While driving a vehicle, a driver of the vehicle needs to visually identify objects such as other vehicles, persons on the road, marking lines on the road surface, roadside structures and drive the vehicle in accordance with the results of the identification of the objects. For example, during driving, upon spotting an elongate vertically-standing object ahead and slightly toward left in the direction of forward movement, the driver needs to determine whether the object is a utility pole or a pedestrian. If the object is a pedestrian or the like, the driver needs to take action, for example, to drive slowly. However, under adverse conditions such as rainy weather or nighttime, spotting, in the field of view, an object in front of the vehicle is difficult. Determining what the object is more difficult.
Thus, mounting of an active visibility support apparatus in a vehicle has been examined to facilitate the identification of an object expected to be present in the driver's field of view. The active visibility support apparatus illuminates the front of the vehicle with near infrared light or the like to acquire an image of a scene in the direction of forward movement as seen from the vehicle, thus allowing the driver to easily determine what each of the objects in the image is. Reflection spectrum is expected to vary with the type of the object. Thus, to allow an object to be identified, it has been proposed to acquire a plurality of images for different wavelength bands by using a multiband camera or the like to identify the object.
As described in JP2005-115631A, compared to normal color cameras that use filters corresponding to the three primary colors, that is, the three wavelength bands, the multiband camera offers wavelength bands that are individually narrow. The multiband camera further includes a large number of such wavelength bands to allow images to be acquired for the respective individual wavelength bands. A typical multiband camera includes several to several tens of wavelength bands. Because of the large number of wavelength bands, the use of the multiband camera allows the spectrum of light from each point on the object to be reproduced, though the accuracy of the spectral reproduction is low. JP2005-115631A discloses an image display apparatus which uses a multiband camera to acquire images on one of which a user specifies a range to allow the spectrum of the range to be displayed in a graph or which calculates and displays an image for a particular wavelength when the wavelength is specified.
JP2001-099710A illustrates a multiband camera with a single imaging device, for example, a CCD (charge-coupled device) sensor, which uses, for example, a liquid crystal tunable filter capable of controlling a transmissive wavelength band, to switch the transmissive wavelength in order to take images for a plurality of wavelength bands. JP2001-099710A also illustrates a technique to compensate for a deviation from a set value for the spectral transmission characteristics of the tunable filter and to estimate the spectrum of an object at a finer wavelength resolution from images for a plurality of wavelength bands.
JP11-096333A illustrates a technique to estimate the spectrum of an object at a finer wavelength resolution from images for a plurality of wavelength bands taken by a multiband camera, similarly to JP2001-099710A. JP11-096333A also discloses the use of a rotary filter for switching a band for imaging when a single imaging device is provided.
When an object is illuminated with light and an image of reflected light from the object is taken, images for a plurality of wavelength bands can be acquired by using, as an illumination light source, a plurality of light emitting diodes (LEDs) each with narrow-band emission spectral characteristics to take images of the object with the wavelength of the illumination light varied.
Furthermore, as an example of identification of an object in a large number of images for a large number of wavelength bands obtained by a multiband camera, a hyper spectral sensor with more wavelength bands, or the like, JP2008-152709A discloses a method of examining what covers the surface of the ground based on a large number of hyper spectral images. This method examines whether the target surface of the ground is, for example, a road or a water surface or is covered with plants, and if the surface of the ground is covered with plants, examines the distribution of vegetation. The method according to JP2008-152709A presets a combination of a plurality of wavelength bands suitable for classification of areas according to classes of roads, forests, and the like to allow an extraction target area to be automatically selected. For example, learning with supervised data is used to set the classes. Then, only images for a plurality of wavelength bands corresponding to classes to be extracted are preselected. The target area is then identified in the selected images.